Power conversion device

Abstract

A power converter includes at least one arm having a plurality of converter cells cascaded to each other. Each of the converter cells includes a pair of input/output terminals, a plurality of switching elements, and a power storage element. The power storage element is electrically connected to the input/output terminals through the switching elements. A control device generates a control signal for controlling on and off of the switching elements of each converter cell. The control device generates the control signal by pulse width modulation control based on a modulation command signal including an AC component having a fundamental frequency and corresponding to a command value of an output voltage between the input/output terminals, in each converter cell, such that a harmonic component included in the output voltage and having a predetermined frequency that is an integer multiple of the fundamental frequency is suppressed.

The invention claimed is: 
     
       1. A power conversion device comprising:
 a power converter including at least one arm having a plurality of converter cells cascaded to each; and 
 a control device to control the power converter, 
 each of the converter cells including
 a pair of input/output terminals, 
 a plurality of switching elements, and 
 a power storage element electrically connected to the input/output terminals through the switching elements, 
 
 the control device including
 an individual cell controller to generate a control signal for controlling on and off of the switching elements of each of the converter cells, 
 
 wherein the individual cell controller generates the control signal by pulse width modulation control based on a modulation command signal including an AC component having a predetermined first frequency and corresponding to a command value of an output voltage between the input/output terminals, in each converter cell, such that a harmonic component included in the output voltage and having a predetermined frequency that is an integer multiple of the first frequency is suppressed. 
 
     
     
       2. The power conversion device according to  claim 1 , wherein
 the individual cell controller includes
 a carrier signal generator to generate, as a carrier signal, a periodic signal having a second frequency higher than the first frequency and a reference phase, and 
 a signal generator to generate the control signal based on comparison between the carrier signal and the modulation command signal, 
 
 the second frequency is determined in accordance with a first integer and a second integer selected such that an integer multiple by the first integer of a first period that is a reciprocal of the first frequency is equal to an integer multiple by the second integer of a second period that is a reciprocal of the second frequency and that integer multiples of the first period by all integers smaller than the first integer are non-integer multiples of the second period. 
 
     
     
       3. The power conversion device according to  claim 2 , wherein
 the first integer is further selected such that a ratio of an amplitude of the harmonic component having the predetermined frequency to an amplitude of a component having the first frequency of the output voltage is equal to or smaller than a predetermined threshold value. 
 
     
     
       4. The power conversion device according to  claim 2 , wherein the first integer is selected such that a ratio of a time average value of the ratio of the amplitude of the harmonic component having the predetermined frequency to the amplitude of an component having the first frequency in a predetermined period is equal to or smaller than a predetermined threshold value. 
     
     
       5. The power conversion device according to  claim 2 , wherein
 the first integer is further selected to be an integer multiple of the number of the converter cells of each arm. 
 
     
     
       6. The power conversion device according to  claim 2 , wherein
 the first integer is selected to be an even number equal to or greater than four. 
 
     
     
       7. The power conversion device according to  claim 6 , wherein the second frequency is set by selecting a power of two that is equal to or greater than four as the first integer. 
     
     
       8. The power conversion device according to  claim 1 , wherein
 the individual cell controller includes
 a carrier signal generator to generate, as a carrier signal, a periodic signal having a second frequency higher than the first frequency and a reference phase, and 
 a signal generator to generate the control signal based on comparison between the carrier signal and the modulation command signal, and 
 
 the carrier signal generator generates the carrier signal such that at least one of the second frequency and the reference phase fluctuates with time during operation of the power converter. 
 
     
     
       9. The power conversion device according to  claim 8 , wherein the carrier signal generator generates the carrier signal such that the second frequency fluctuates with time during operation of the power converter. 
     
     
       10. The power conversion device according to  claim 8 , wherein the carrier signal generator generates the carrier signal such that the reference phase fluctuates with time during operation of the power converter. 
     
     
       11. The power conversion device according to  claim 8 , wherein the control device performs control such that the carrier signal generator generates the carrier signal such that at least one of the second frequency and the reference phase fluctuates, in accordance with a history value of voltage variation of the power storage element, during operation of the power converter. 
     
     
       12. The power conversion device according to  claim 8 , wherein the carrier signal generator generates the carrier signal with at least one of the second frequency and the reference phase fluctuated, such that a time average value of a ratio of an amplitude of the harmonic component having the predetermined frequency to an amplitude of a component having the first frequency of the output voltage is equal to or smaller than a predetermined threshold value. 
     
     
       13. The power conversion device according to  claim 8 , wherein the carrier signal generator generates the carrier signal with at least one of the second frequency and the reference phase fluctuated, such that a time average value in a certain period of a ratio of an amplitude of the harmonic component having the predetermined frequency to an amplitude of a component having the first frequency of the output voltage is equal to or smaller than a predetermined threshold value. 
     
     
       14. The power conversion device according to  claim 1 , wherein
 the modulation command signal is indicated by a sum of a DC component and an AC component having the first frequency, 
 the individual cell controller includes a signal generator to generate the control signal in accordance with a pulse pattern signal in which a plurality of pulses are provided in each of predetermined pattern periods, 
 on and off of the switching elements of each converter cell is switched at each of both edges of each of the pulses, 
 the pattern period is an integer multiple of a first period that is a reciprocal of the first frequency, 
 some of the edges of the pulses are set to phases in the pattern period for controlling the DC component and an amplitude and a phase of the AC component, and 
 others of the edges are set to phases in the pattern period for suppressing a harmonic component having the predetermined frequency. 
 
     
     
       15. The power conversion device according to  claim 14 , wherein
 the pulse pattern signal is generated such that the pattern period is twice the first period and to have at least four of the pulses in each pattern period, and 
 the phases of four edges among the edges are set to suppress harmonic components having frequencies five times and seven times the first frequency. 
 
     
     
       16. The power conversion device according to  claim 1 , wherein the harmonic components suppressed at least include a frequency five times, a frequency seven times, a frequency 11 times, and a frequency 13 times the first frequency. 
     
     
       17. The power conversion device according to  claim 1 , wherein
 each of the converter cells further includes
 a voltage detector to detect a voltage of the power storage element, the control device further includes 
 a voltage command generator to set, as a voltage command value for the arm, an average value of voltage detection values by the voltage detector in the converter cells for each arm, 
 
 the individual cell controller includes
 a voltage controller to calculate a control output based on a deviation between the voltage detection value in each converter cell and the voltage command value, and 
 
 the modulation command signal reflecting the control output from the voltage controller is generated. 
 
     
     
       18. The power conversion device according to  claim 1 , wherein the power converter is connected between a DC circuit and an AC circuit to mutually convert DC power and AC power.